The field of art to which this invention is directed is aromatic amine curing agents for polyepoxide resins, particularly hindered aromatic amines accelerated with metal fluoborates.
Aromatic amines are well known curing agents and are discussed in detail in many technical publications, e.g., "Epoxy Resins" by Lee and Neville (1957). Typical aromatic amines, used as curing agents, are meta-phenylene diamine, methylene dianiline and diaminodiphenyl sulfone. Such amines are solid compounds which must be heated when mixed with polyepoxide resins. Curing temperatures and curing times are relatively high and long but can be reduced somewhat with an accelerator, e.g., a phenolic compound, aliphatic amine or boron trifluoride amine complex.
The use of hindered aromatic amines as curing agents for epoxy resins is also knonw. U.S. Pat. No. 4,366,108 describes curable compositions made from a liquid epoxy resin, a hindered aromatic amine, namely, diethyltoluenediamine, and a curing accelerator. Typical accelerators are 1-methylimidazole, phenols, salicylic acid and boronfluoroamine complexes, such as BF.sub.3 -acetoacetanilide, BF.sub.3 -aniline complexes or BF.sub.3 -monoethylamine.
Metal fluoborates, or fluoborate salts, are known to be curing agents for polyepoxide resins as described in U.S. Pat. No. 3,432,440. The curing agent described in this patent is a mixture of a fluoborate salt, e.g., zinc fluoborate in aqueous solution; a carrier liquid, e.g., polyethylene glycol; and a hydrolyzable ester, e.g., triphenyl phosphite.
Various metal fluoborates are used to catalyze the curing of epoxy compounds in U.S. Pat. No. 3,018,262. Complex curing systems involving zinc fluoborate complexes, polyols and polycarboxylic acid anhydrides are described in U.S. Pat. No. 4,321,351.